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Heating Bathroom Floors on the cheap

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Posted by slow_mac_modem on August 30, 2005, 1:22 pm
What keeps me from taking a 1/8" plastic tube, looping it around the
bathroom floor, putting a thin layer of thin set mortar over it, laying
tile on top, connecting one end of the tube to the hot water tap, the
other to the cold water tap and turning it on/off via a program on my
Macintosh connected to a USB experiment board connected to a 110v relay
that turns on a small pump?

Total cost perhaps $50 for 100 sq ft coverage.  Seems like this would
be a cheaper way to go than to shell out $00 on an electric mat type
heating system.

Opinions *please*.  

PS - Water is already heated via solar collector.

Posted by Ecnerwal on August 30, 2005, 1:34 pm
 slow_mac_modem@yahoo.com wrote:

1/8" tube has very high pumping power requirements, and very low thermal
capacity - ie, /vs. the typical 1/2" or 3/4" PEX tubing, it will tend to
warm up a few feet of the start of it's run, and then have no more heat
to give. Upsizing the pump will run into limits on fluid velocity, and
eat huge amounts of power (and likely make a lot of noise, too).

Could work if you went to a larger size tubing, (be sure to use PEX -
random "plastic" will probably not hold up as well for the long haul,
and leaking in-floor heat sucks). If you use the cold-water tap as the
return line, you'll have to run the cold water for a while to get cold
water from the tap. A separate return line would eliminate that. Your
pump needs to be bronze or stainless ($$$), since this is open loop in
potable water - a cheap iron pump will rust out.

You're working way too hard  (or expensive) on the switch. If you want a
timer function, off the shelf timers are considerably less expensive
than computer+interface+relay. Thermostats, including thermostats with
timer functions are also easily available off the shelf.

Cats, coffee, chocolate...vices to live by

Posted by Pokey on August 30, 2005, 4:39 pm
Thanks for replying.  What about using 3/8" or 1/2" (can't remember
which one I used on my collector) copper pipe?   Seems like the plastic
tubing may actually act as an insulator.  Copper is used in my
collector and I think it may do a better job than the PEX but I've
never even seen PEX before.  I was thinking plastic because it would be
easier to lay.

I was tring to keep it small.  The larger you go, the more mortar is
required to cover it all.  Then it has to be leveled.  I'm not sure
thin set is made to go on that thick.

I actually already have an auto-cerc pump that would probably do the
job well.  It is set to maintain the temp at 90 F and it has a timer.

Posted by Ecnerwal on August 30, 2005, 8:24 pm
PEX is a particular type of plastic - cross-linked polyethylene - it is
made for this job. Drop "radiant floor heat" into any search engine and
read to your heart's content.

Copper in (tile/masonry/concrete) floors corrodes and leaks. Has been
done, very common in the 1950's, one reason anyone who remembers that
era is very suspicious about radiant floor heat.

Cats, coffee, chocolate...vices to live by

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